<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
	<canvas id="canvas" width="400" height="300">
		不支持canvas
	</canvas>
	<script>
		var canvas = document.getElementById('canvas');
		var ctx = '';
        ctx = canvas.getContext('2d');
		ctx.beginPath();
		ctx.moveTo(20,20);           
		ctx.lineTo(100,20);          
		ctx.arcTo(150,20,150,70,50); 
		ctx.lineTo(150,120);         
		ctx.stroke(); 
	</script>
		
	</body>
</html>
